Chairs having mechanisms permitting tilting of the chair backs, normally being biased in upright positions, are disclosed in U.S. Pat. Nos. to Faiks et al. 4,390,206, issued Jun. 28, 1983; Knoblauch et al. 4,373,692, issued Feb. 15, 1983, and 4,438,898 issued Mar. 27, 1984; Faiks 4,314,728, issued Feb. 9, 1982; Fox 2,686,558, issued Apr. 27, 1950; Fries et al. 4,479,679, issued Oct. 30, 1984; Neuhoff 4,537,445, issued Aug. 27, 1985; Eldon III 4,328,943, issued May 11, 1982; McLellan et al. 2,272,980, issued Feb. 10, 1942; Scherer 2,956,619, issued Oct. 18, 1960; Cramer 2,471,024, issued May 24, 1949; and Franck et al. 4,451,085, issued May 29, 1984. Some of these patents disclose chairs having control means for adjusting tension of biasing means normally urging the chair backs in the upright positions. See, for example, Faiks et al., Knoblauch et al., Faiks, Scherer, Cramer, Fries et al., and Eldon III.